The performance of semiconductor devices has been improved mainly because of the downscaling of circuit patterns. Since the dimensions and shapes of fine patterns greatly affect the performance of devices, it is necessary to perform inspection highly accurately in high resolution. Therefore, at the manufacturing sites of semiconductor devices, a critical dimension scanning electron microscope (CD-SEM) is used for pattern inspection.
The CD-SEM applies a narrowly focused electron beam onto a specimen, and calculates the dimensions and shapes of a pattern formed on the specimen from the intensity distribution of backscattered electrons or secondary electrons emitted from the applied location for determining whether the pattern is good or bad.
FIGS. 1A to 1C are diagrams for explaining the detection of pattern edge positions. FIG. 1A illustrates the cross sectional topology of a line pattern, FIG. 1B illustrates a schematic diagram depicting an image obtained when observing this line pattern using a CD-SEM, and FIG. 1C illustrates a signal intensity distribution. Since the amount of secondary electrons emitted is increased at pattern edge portions, which is called edge effect, a band-like region called a white band is observed at a location corresponding to a pattern edge portion in an image obtained by the CD-SEM (two white vertical lines in FIG. 1B). This white band is used for detecting a pattern edge position.
There are proposed various signal processing algorithms for identifying pattern edge positions, and which algorithm is used for detecting edge positions is decided mainly by a user. For exemplary edge detection algorithms, Patent Literature 1 discloses a waveform matching method, and Non-Patent Literature 1 discloses a function fitting method or the like.
Moreover, a signal intensity waveform is used not only for detecting edges but also for estimating the cross sectional topology of a pattern as described in Patent Literature 2. Furthermore, Patent Literature 3 describes an automatic determination method for false dimension measurement due to defocus from the slope of a signal intensity distribution.